10 Tell-Tale Signs That He's Cheating [EXPERT]

He's acting differently, but you just can't put your finger on why. Then, his cell phone rings in in the middle of the night, and he doesn't have a good explanation. Is he cheating or is he just going through a rough time?

We've all heard the "he blames you for cheating" and "his cell phone has a password on it" behaviors of cheating men, but those are the obvious shifts. After interviewing 50 cheating men — and a number of their wives/ex-wives — there are several subtle changes that can take place and that women are usually unaware of until it's too late. Here are the top 10 tell-tale signs to watch for in your man.

1. He strays from his predictable everyday behavior.

"My wife knew I was cheating before there was any real evidence. She said should could just tell."

After spending time with someone for a number of months (or even years), you know their typical behavior. You know how they will act in certain situations and when they act differently, there has to be an explanation — if not cheating, then something else real and tangible. In this respondent's case, he wasn't doing anything strange, but he explained the sign that exposed him. When he started his affair, he would grab his phone and head into the restroom for 20-30 minutes. His excuse: He was "reading email and the news." The only problem was, his phone bill showed something very different.

2. He has unpredictable mood swings.

"I was constantly looking for reasons to get away, and it was hard to think of new excuses all the time. So, I'd start a fight with her."

Being angry instantly — or being overly nice — is a red flag. There's no real reason for him to leave, so he has to create one. New activities that he goes to all the time, but never mentions is a glaring example. If he was going somewhere and had no reason to hide it, he would most likely share it with you. ("I need time just to be alone.") While logical, excuses like these are usually without a reason or completely out of the norm for him.

3. He has a rapid change in weight or appearance.

"After I started my affair, I dropped like 10 pounds in about a week. It was crazy."

Cheating men change physically. Their love handles disappear, their posture changes and their muscle tone/definition returns. It's the body's primal means of preparing for courtship — he's readying himself to attract a mate. In addition, they start taking much better care of themselves and take a lot of pride in their appearance. He's suddenly pressing his clothes, coiffing his hair and shaving daily when he didn't before... especially when leaving the house without you.

4. He has an overnight change in musical taste.

"I've never really liked jazz. But I struck up with this woman, we enjoyed it together. I started listening to it all the time, just to think about her."

There's nothing wrong with trying new things. But when it's out of the blue and your significant other isn't exposed to the change, it's a warning sign that something is amiss.

5. He remembers things wrong or loses track of the details.

"I was talking to my wife about a movie we saw and laughing about one of the scenes. She wasn't laughing. I asked, 'What? Don't you remember?' She then informed me that we hadn't see it together."

As he spends more time with both of you, the memories of his time spent with his mistress and the memories of his time spent with you will start to blur together. Schedules get crossed and he won't be able to keep track of where he was on any given day. The time he spent with another woman will be unaccounted for — often, with no explanation.

6. He needs lots of privacy.

"I was working from home and I started closing the door more often, saying that the kids were loud or that I just needed to work quietly. I was online chatting with my mistress."

To take time for one's self is normal. But when it's out of the normal pattern—or is more and more frequent—it's a sign that something else is going in. Going into work early, leaving late, getting off the phone suddenly, taking lots of private calls from a "relative" (mom, sister, someone untrackable) are also red flags.

7. He has a drastic change in sexual appetite and style.

"I started my affair and all I wanted was sex, but not from my wife. She knew something was up, because our sex life was always pretty active."

"After I started up with [my mistress], I started sleeping with my wife much more often. She told me I was really aggressive in bed and that she hadn't seen me that way before."

A sudden shift in what's "regular" or familiar in bed — without a discussion of wanting something new — is a big warning sign of cheating. All of the interviewed men expressed having the feeling of a huge rush of testosterone — which would manifest as a new confidence during sex. They felt strong, masculine, the embodiment of virility and like every woman wanted them. Their egos were growing daily.

8. He hides his financial history from you.

"I was meeting [her] for lunch almost daily. And our hotel visits were three or four times per week. Covering that was very difficult. I opened a PayPal account, got a PayPal debit card and attached a personal checking account to [my PayPal account]. I would make online transfers into PayPal and she couldn't see any of my transactions."

Most cheating men will need an untraceable way to pay for things: gifts, meals, hotels, trips, etc. Refillable credit cards, PayPal accounts, eBay purchases are all great ways to try and hide large or frequent transactions. Large, random transfers or cash withdrawals should be investigated.

9. He has new "friends" at work and/or more work responsibilities.

"My company allowed me to work from home if I choose. But I had started a relationship with a new manager at the office, so I started going in to work more often. Extending my business trips a day before or after I was needed at a remote site, extended office lunches and late hours."

Office affairs are very common, especially considering how much time we spend working together. He might mention his new "friend" to dispel any suspicions you have and if you pop in to the office unexpectedly, he might even introduce you to his "coworker" to throw you off the scent. Follow your gut and pay attention to his other behaviors.

10. He's secretive with his technology.

"Messages on the iPhone are untraceable on cell phone bills. I would only text [my mistress] when it was safe and then delete the messages immediately. To this day my wife doesn't know how I communicated with [my mistress]."

"I didn't want to send email because it can be traced. So, we got a new Gmail account and communicated in the drafts folder, without sending anything."

Technology has gotten smarter and affairs have gone high-tech. The signs used to be a new password on a cellphone or computer, a change in the password at your bank or cellphone company or cellphones being "left in the car." But now, cheaters can fly under the radar by using technology to do their communication dirty work. Apps exist that allow text messages, online chat sessions and pictures to last for a certain amount of time (and then disappear). Pay attention to new email accounts and new apps being used on his cell phone.

While these signs aren't foolproof signs of cheating, a few taken in combination are sure signs that something is up. Advice: don't make accusations that you can't back up. If you suspect it, sit him down for a long talk about your concerns. If that nagging feeling doesn't disappear, you have some choices to make — and perhaps some investigations to start.